ROLE OF ERYTHROID KRUPPEL-LIKE FACTOR IN HUMAN GAMMA-GLOBIN TO BETA-GLOBIN GENE SWITCHING

Erythroid Kruppel-like factor (EKLF) is an erythroid-specific transcri ption factor that contains zinc finger domains similar to the Kruppel protein of Drosophila melanogaster. Previous studies demonstrated that EKLF binds to the CACCC box in the human beta-globin gene promoter an d activates transcription. CACCC box mutations that cause severe beta- thalassemias in humans inhibit EKLF binding. Results described in this paper suggest that EKLF functions predominately in adult erythroid ti ssue. The EKLF gene is expressed at a 3-fold higher level in adult ery throid tissue than in fetal erythroid tissue, and the EKLF protein bin ds to the human beta-globin promoter 8-fold more efficiently than to t he human gamma-globin promoter. Co-transfection experiments in the hum an fetal-like erythroleukemia cell line K562 demonstrate that over exp ression of EKLF activates a beta-globin reporter construct 1000-fold; a linked gamma-globin reporter is activated only S-fold. Mutation of t he beta-globin CACCC box severely inhibits activation. These results d emonstrate that EKLF is a developmental stage-enriched protein that pr eferentially activates human beta-globin gene expression. The data str ongly suggest that EKLF is an important factor involved in human gamma - to beta-globin gene switching.